The present invention relates generally to digital watermarking of host signals, such as audio signals, video signals, and images. More particularly, the present invention relates to using the relative position of watermarks within a host signal to represent embedded information. Methods and apparatus are provided for embedding the information in the host signal based on the relative position of watermarks within the host signal. Corresponding methods and apparatus are provided for extracting the embedded information from the host signal based on the relative position of watermarks within the host signal. Computer readable medium are provided for carrying a watermarked host signal with the embedded information. The positioning of digital watermarks can be used, for example, to embed copy-control and/or media verification information in an audio or video host signal without degrading the quality of the audio or video output.
A number of distinct prior art watermarking technologies have been proposed and/or patented. These prior art technologies achieve different levels of transparency (fidelity, or non-perceptibility), robustness to standard host-signal processing, tamper resistance, implementation cost, throughput (amount of embedded information), false positive rate, and watermark layering potential.
Watermarks can be used to provide copy control of the original content. For example, copy-control information may be embedded in a host signal so that unauthorized copying of the host signal is prevented. Watermarks can also be used to provide media verification. Media verification watermarks provide information verifying that the content (i.e. of a CD, DVD, or the like) is original content which can be presented for distribution or a copy of the content which cannot be presented for distribution. Media verification also refers to verifying that a user can present entire original content, without any cuts, before a piece of content is copied. Media verification is specifically designed to make distribution of content over the Internet more difficult, for example, by requiring a user to download an entire CD in one piece, even if only one song is desired. Besides copy-control and media verification information, watermarks can carry information that identifies the content, rightful owner, distributor, recipient, and the like.
In all cases, distinct embedded messages are represented by distinct watermarks, i.e. the watermark itself is the vehicle that carries the information.
It would be advantageous to use the position of the watermarks embedded in the host signal as a vehicle that carries embedded information. It would be further advantageous to use the relative position among two or more watermarks as a vehicle that carries the embedded information. It would be further advantageous to provide for the relative positioning of the watermarks to carry information relating to copy-control and media verification.
The methods and apparatus of present invention provide the foregoing and other advantages.